GE/FE Head Differences

There are generally two types of cylindar heads that Toyota uses in its gas-powered vehicles. These are represented in the engine code (all-non RWD Celicas) by either a F or a G in the engine code. The F-head (high efficency below) has a design which optimizes mid range torque/horsepower. The G-head (high performance), in contrast, produces significantly more horsepower but at a much higher RPM. Since most driving takes place between 500-4000RPMs, the F-head holds the drivability and mileage advantage over the GE head. As such this design shows its dominance in most Toyota vehicles in the US. When it comes to performance the G-head will is superior hands down.The following diagrams from the book "Toyota Engine Technology" published by Toyota in 1989 illustrate the differences in Toyota's data between the two engines.

Physical Differences

As you can see in this image the G-head is designed with a wider valve angle (50° as opposed to 22-25°) and a different shaped squish area

This image illustrates the side profiles of the 3S engine block with the G- & F-heads. The size difference is most likely due to the slave-twin cam design of the F-head as opposed to the true twin cam design of the G-head.

Performance Differences:

This is the torque curve of a F-head (high-efficiency twin cam) as opposed to a G-head (Sports-type twin cam).

Again, the power differences between the F-head(middle) and G-head engines. I believe this graph illustrates the various Toyota engines with either head (circa 1989).

all images from Toyota Engine Technology ©1989 Toyota